INVITATION TO ASTRONOMY

Astronomy is the science that studies the things we see in the
far sky: stars, planets, asteroids, comets, nebulae, galaxies
and many other strange objects that have been discovered since
Galileo first turned a telescope toward the heavens 400 years
ago.

Although professional astronomers use equipment that can be
very expensive, the universe is at your back door and to study
it doesn't have to cost a lot. There are between 2000 and
3000 stars visible in the night sky to the unaided eye, and
even a small pair of binoculars can show an amazing amount
of detail and objects not visible to the eye.

Learning your way around the sky is a good way to start. And
if you wish to look further there are observatories and
planetariums that are open to the public and staffed by
people only too eager to talk about their interests.

2009 is the international year of astronomy. This is a good
time to learn more about the Universe in which you live. Explore the night sky and expand your horizons.

Some goals you might like to set yourself:

Learn the names of 10 stars

Be able to identify 5 constellations

Learn the name of 5 features on the Moon

Visit an observatory or planetarium

Learn the names of 5 astronomers

Observe 10 meteors or satellites

Your explorations will be enhanced if you keep a notebook of what you did and when. This also helps you to build your
knowledge as time goes by, and is a valuable reference source.

STARS

Stars make up the majority of the objects that we see in
the night sky. Stars are really suns, and our Sun is a star.
Stars appear much fainter than the Sun simply because they
are much further away.

Stars differ in brightness for two main reasons, their
intrinsic brightness and their distance from the Earth.
Stellar distances and huge and are measured in light years,
which is the distance light travels in one year. This is
9.5 trillion (million million) kilometres. When we look at a star we see how it was in the past, not how it is now.
All the stars we see in the night sky are in our own galaxy, the milky way, and are thus relatively close compared to the
overall size of the universe.

Stars not only vary in brightness but also in colour.
The colour depends on the temperature of the star,
which varies from 2000 to 50,000 Celsius.
Stars are classified by their colour into alphabetic types.
We can remember the order by the
first letter of each word in the phrase "Oh, Be A Fine Girl,
Kiss Me". The Sun is a G-type star, right in the middle, with
a temperature of 6000 degrees.

Variable stars vary in brightness. Binary stars are two stars
close to and often orbiting each other. Astronomers think that about half of all stars are binary, even though we can't
see this with our eyes (because most binaries stars are too
close together).

The brightest stars have mainly Arabic names.

To make it easier to find one's way around the sky, stars
are grouped into 88 'constellations' which have mostly Greek
or Latin names. Not many of these groupings resemble the name
given to them, but some do, for example the 'southern cross'
and 'scorpius' the scorpion.

PLANETS

Although most stars appear fixed in the sky (although the
night sky as a whole appears to move around the Earth), there
are five bright objects that we can see wandering around the other stars. These are the planets, and they are much closer
to us than any other star we see in the night sky. They are
bound to the Sun by gravity, along with the Earth and other
planets too faint to see. Together, they form the solar
system.

These images, taken by the Hubble Space Telescope, show three of the planets visible to the naked eye. [STScI/NASA/ESA]

Mars, showing its red deserts and icy polar cap.

The solar system also contains a large number of smaller bodies: asteroids, comets and meteoroids.

Comet Hyakutake

Some other stars have planets around them, and astronomers
are currently trying to find more, particularly planets that
might be like Earth.

TELESCOPES AND OBSERVATORIES

Telescopes vastly improve our view of the universe in which
we live. Telescopes are often housed in buildings we call
observatories.

Perth Observatory

Skymapper at Siding Spring

However, not all telescopes are the traditional optical
telescopes. Many radio telescopes are now used to map the
radio signals from celestial objects.

A low frequency radio telescope using many small antennae.

Some telescopes are sent into space, to avoid the bad effects of the Earth's atmosphere. Some types of astronomy (X-ray and gamma ray astronomy) can only be conducted from space.

This is a picture of the Hubble Space Telescope taken by NASA astronauts after its final servicing mission by the Space Shuttle.

STRANGE AND BEAUTIFUL

Stars and planets are of course not the only things in the sky. The glow of light across the sky known as the milky
way is the vast collection of stars that make up our galaxy.
Although we cannot directly see the shape of our galaxy, we can see other galaxies, and radio astronomical evidence leads
us to believe that it is like some spiral galxies, as shown below.

M74

M51

Within our galaxy we can see many patches of fuzzy light we
term nebulae. When examined with large telescopes these often show beautiful shapes and colours. Many nebulae are believed
to be the aftermath of a dead or dying star. The ones shown
below are the cat's eye and the butterfly nebulae.

All imagesin this sectionare from the
HubbleSpaceTelescope[STScI/
NASA/ESA]

Many other strange and fantastic objects are known, while some
are waiting for us to discover them. Many observatories and
organisations make their images available via the world wide
web.